Hardness Conversion Chart

Hardness scales measure slightly different things — Rockwell C uses a diamond cone and reads directly, Brinell presses a 10 mm ball and measures the impression diameter, Vickers uses a pyramidal diamond at very light loads. Conversions between them are approximate and apply mainly to carbon and low-alloy steels; high-alloy, austenitic stainless, and non-ferrous metals need their own tables. Tensile strength (ksi / MPa) is an empirical estimate from Brinell — useful for quick material sanity checks, not certification.

High-range (HRC) steel — ASTM E140 Table 1

HRC	HV	HBW (3000 kgf)	HRA	Tensile ksi	Tensile MPa
68	940	—	85.6	—	—
66	865	—	84.5	—	—
64	800	—	83.4	—	—
62	746	—	82.3	—	—
60	697	—	81.2	—	—
58	653	—	80.1	351	2420
56	613	—	79.0	325	2240
54	577	—	78.0	301	2075
52	544	—	76.8	279	1920
50	513	—	75.9	259	1785
48	484	—	74.7	241	1660
46	458	—	73.6	225	1550
44	434	409	72.5	210	1450
42	413	390	71.4	197	1360
40	392	371	70.4	185	1275
38	372	353	69.4	175	1205
36	354	336	68.4	164	1130
34	336	319	67.4	155	1070
32	318	301	66.3	146	1010
30	302	286	65.3	138	950
28	286	271	64.3	131	900
26	272	258	63.3	124	855
24	260	247	62.4	118	810
22	248	237	61.5	113	780
20	238	226	60.5	108	745

Mid-range (HRB) steel — ASTM E140 Table 2

HRB	HV	HBW (3000 kgf)	HRC (est.)	Tensile ksi	Tensile MPa
100	240	228	20	110	760
98	228	216	19	104	715
96	216	205	17	98	675
94	206	195	15	93	640
92	196	185	13	88	605
90	187	176	11	84	580
88	179	169	9	80	550
86	171	162	7	77	530
84	165	156	5	73	505
82	158	149	3	70	485
80	152	143	—	67	460
78	147	138	—	65	450
76	142	133	—	63	435
74	137	129	—	61	420
72	133	125	—	59	405
70	129	121	—	57	395
68	126	118	—	56	385
65	120	113	—	53	365
60	109	103	—	48	330
55	100	95	—	44	305
50	92	87	—	41	285

Typical hardness of common materials

Material	Condition	HRC / HRB	HBW	Tensile
Pure aluminum	Annealed	HRB 15	25	10 ksi
6061-T6 aluminum	T6	HRB 60	95	45 ksi
7075-T6 aluminum	T6	HRB 87	150	83 ksi
Copper	Annealed	HRB 30	45	32 ksi
Brass 360	Half-hard	HRB 78	120	58 ksi
Mild steel 1018	Cold-rolled	HRB 72	126	65 ksi
Steel 1045	Hot-rolled	HRB 95	180	91 ksi
Steel 4140	Annealed	HRB 95	200	95 ksi
Steel 4140	Quench & temper	HRC 30	286	135 ksi
Steel A2 / D2	Hardened	HRC 58-62	—	—
Stainless 304	Annealed	HRB 82	150	75 ksi
Stainless 17-4	Cond. H900	HRC 44	400	190 ksi
Tool steel M2	Hardened	HRC 62-65	—	—
Titanium Ti-6Al-4V	Annealed	HRC 36	334	138 ksi
Cast iron (gray)	As-cast	HRB 90	190	30 ksi*
Ductile iron	As-cast	HRB 95	220	75 ksi
Diamond	—	HRC 100+	~10000	—

Scale selection guide

HRC	Hardened steel (Rc 20-70). Diamond brale, 150 kgf. Standard for tool steel, bearings, shafts.
HRB	Soft steel, brass, aluminum (HRB 30-100). 1/16" ball, 100 kgf. Too soft for HRC.
HRA	Very hard thin case-hardened parts (HRA 60-85). Diamond, 60 kgf. Less penetration than HRC.
HRN	Superficial Rockwell for thin sheet / surface layers. 15N, 30N, 45N scales.
HBW	Brinell with tungsten-carbide ball (10 mm), 3000 kgf for steel / 500 kgf for soft metals. Best for averaging through coarse microstructure.
HV	Vickers pyramidal diamond, micro-indentation (10 gf to 10 kgf). Single continuous scale covering everything from gold leaf to carbide.
Knoop (HK)	Elongated diamond for measuring very thin coatings or brittle materials. Most common in micro-hardness labs.

Tips & cautions

Conversions are valid for carbon and low-alloy steels. For stainless, aluminium, brass, cast iron, and hardened ceramics use material-specific tables.
HRB readings are invalid above about 100 — use HRC. HRC readings below 20 are invalid — use HRB.
Case-hardened parts have a thin hard surface over a softer core. Use HRN superficial scales or measure a cross-section after sectioning / polishing.
The "tensile" column is an approximation: UTS (ksi) ≈ HBW / 2 for low / medium carbon steels. Use actual tensile data for spec-critical work.
Typical shop comparator: a sharp file will skid across HRC 60+ steel; a "hard-file test" is a go / no-go check around HRC 55-60.

Notes

Data compiled from ASTM E140-12b (Standard Hardness Conversion Tables for Metals). For aluminum-specific conversions consult ASTM B648; for stainless consult the supplier datasheet.

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HRB	HV	HBW (3000 kgf)	HRC (est.)	Tensile ksi	Tensile MPa
100	240	228	20	110	760
98	228	216	19	104	715
96	216	205	17	98	675
94	206	195	15	93	640
92	196	185	13	88	605
90	187	176	11	84	580
88	179	169	9	80	550
86	171	162	7	77	530
84	165	156	5	73	505
82	158	149	3	70	485
80	152	143	—	67	460
78	147	138	—	65	450
76	142	133	—	63	435
74	137	129	—	61	420
72	133	125	—	59	405
70	129	121	—	57	395
68	126	118	—	56	385
65	120	113	—	53	365
60	109	103	—	48	330
55	100	95	—	44	305
50	92	87	—	41	285

HRB	HV	HBW (3000 kgf)	HRC (est.)	Tensile ksi	Tensile MPa
100	240	228	20	110	760
98	228	216	19	104	715
96	216	205	17	98	675
94	206	195	15	93	640
92	196	185	13	88	605
90	187	176	11	84	580
88	179	169	9	80	550
86	171	162	7	77	530
84	165	156	5	73	505
82	158	149	3	70	485
80	152	143	—	67	460
78	147	138	—	65	450
76	142	133	—	63	435
74	137	129	—	61	420
72	133	125	—	59	405
70	129	121	—	57	395
68	126	118	—	56	385
65	120	113	—	53	365
60	109	103	—	48	330
55	100	95	—	44	305
50	92	87	—	41	285

HRB	HV	HBW (3000 kgf)	HRC (est.)	Tensile ksi	Tensile MPa
100	240	228	20	110	760
98	228	216	19	104	715
96	216	205	17	98	675
94	206	195	15	93	640
92	196	185	13	88	605
90	187	176	11	84	580
88	179	169	9	80	550
86	171	162	7	77	530
84	165	156	5	73	505
82	158	149	3	70	485
80	152	143	—	67	460
78	147	138	—	65	450
76	142	133	—	63	435
74	137	129	—	61	420
72	133	125	—	59	405
70	129	121	—	57	395
68	126	118	—	56	385
65	120	113	—	53	365
60	109	103	—	48	330
55	100	95	—	44	305
50	92	87	—	41	285